Washington, DC, February 6, 2007 - The U.S. Chemical Safety Board (CSB) is continuing its investigation to determine the root causes of the powerful explosion in Danvers, Massachusetts, which damaged or destroyed dozens of homes and businesses during the early morning hours of November 22, 2006.

A team from the CSB documented at least 100 different examples of blast damage - such as shattered windows or broken beams - throughout the Danvers community. These "blast markers" will be interpreted using computer models in an effort to better understand the nature and the explosive force of the blast.

CSB lead investigator John Vorderbrueggen, PE, said that two fuel sources are under consideration for the blast. "The probable source of fuel for the explosion is vapor from flammable solvents that were used to produce printing inks and paints. On the last work day prior to the accident, a heated mixing tank was filled with 2,000 gallons of printing ink ingredients, including flammable, volatile solvents such as heptane and propyl alcohol. Depending upon the temperature of the tank, solvents could have evaporated during the overnight hours when the facility was unattended, accumulated in the building, and found an ignition source."

Mr. Vorderbrueggen said that natural gas remains under examination as a possible fuel source, in addition to or in lieu of solvent fumes. A high-pressure gas transmission line runs underground a few hundred feet south of the facility, and other low-pressure gas lines are a few hundred feet west and north of the facility. However, the CAI/Arnel building where the explosion occurred had no natural gas supply and had a concrete slab floor.

"Although there is no obvious path into the facility for natural gas, we will continue to evaluate the possibility of a leak into the building." Mr. Vorderbrueggen said company tests detected some methane in nearby soils, at a level several hundred times below the lower explosive limit. However, the CSB has found no evidence of a leak from the high-pressure transmission line, and the source of the traces of methane is not clear.

"We are planning to duplicate the solvent recipe that was in use on November 21, and measure its volatility in the laboratory," Mr. Vorderbrueggen said. "The data will help us understand how long it might take to load the building with different flammable concentrations of solvent fumes under various scenarios, such as a leak, spill, or inadvertent overheating." No conclusion has been reached about the fuel for the explosion, and Mr. Vorderbrueggen said that a final determination was still months away.

"Both CAI and Arnel were aware that the materials they used were flammable, and for that reason had installed safe electrical devices to minimize the possibility of ignition. In any industrial facility, however, it is almost impossible to eliminate all ignition sources. Prevention efforts must focus on avoiding the accumulation of flammable vapors and gases, safely ventilating any that do accumulate, and detecting any dangerous concentrations before a fire or explosion occurs," Mr. Vorderbrueggen said. The CSB investigation will examine whether current national building fire code provisions on handling flammable solvents are fully effective.

CSB Chairman Carolyn W. Merritt said, "Of all the accidents the Board has investigated since its establishment in 1998, the Danvers explosion caused the most severe damage to homes and nearby businesses. This blast was considerably more powerful than might be expected from a manufacturing facility of this type. For that reason, I have asked the staff to review the guidance that is currently available to urban planners and local permitting officials on chemical facility siting to see if it can be improved. Better guidance and separation distances may help protect residents from accidents at new facilities, but for existing facilities the only option is improved prevention."

Ms. Merritt noted that a second serious chemical accident in 2006 - at a concrete products facility near Chicago - likely involved the flammable solvent heptane, which was also used at the Danvers plant. That accident, on June 14, occurred as an operator was heating a flammable liquid mixture in a 2,200-gallon open-top tank equipped with steam coils. A vapor cloud formed and exploded, killing a driver, injuring two other workers, and causing extensive facility damage.

"Flammable solvents are among the most common industrial chemicals, and it is all too easy to overlook their potentially deadly hazards," Chairman Merritt said. "All companies that use flammable solvents should promptly review their operations to ensure that appropriate controls are in place. The use of closed vessels, robust ventilation systems, vapor leak detection systems, and explosion-proof electrical systems are all important for preventing disasters. In addition, companies should evaluate using automated or redundant temperature control systems and should follow general good safety practices, such as using written operating procedures and checklists."

The CSB plans to convene a public hearing in Danvers in early April to present preliminary findings and receive comments from community members. Public comments will be considered as the Board continues its investigation and develops its final report and safety recommendations.

The CSB is an independent federal agency charged with investigating industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in safety regulations, codes, standards, management systems, training, and industry practices.

The Board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. For more information, please visit our website, www.csb.gov.